This methodical paper discusses the procedure for developing the farm sustainability index using data from surveys and accountancy data collected in the FADN system database. The research covered a total of 600 farms selected similarly to the selection method used in FADN (taking into account the economic size, production type and region). The structure of the sustainability index of farms uses variables characterizing the environmental, economic and social dimension of sustainability. In total, over 100 output parameters classified in 7 partial indices were used in the assessment of sustainability. The resultant distribution of individual partial indices and dimensions of sustainability indicates the diversity of the studied population in terms of considered parameters. At the same time, it was found that aggregation leads to the dominance of values close to the middle of the range of considered indices. The applied methodology allows to assess the sustainability of individual farms and their classification into groups of entities diversified by the degree of compliance with the principles of sustainable agriculture. The ability to measure and assess the sustainability of farms can be considered as the first step in the process of creating effective agricultural development support policies. The paper provides an opinion in the long-lasting discussion on the operationalization of the concept of sustainable development and ways to measure the degree of compliance of economic operators’ actions with the paradigm in question.